The purchase comes as the microblogging service looks to broaden its appeal for average Internet users while also making its tools better for more experienced tweeters. TweetDeck’s users are clearly in the latter camp.

“This has always been our core audience – the most active, influential and valuable users of Twitter and social media in general,” TweetDeck founder Iain Dodsworth wrote in an official blog post about the deal.

Twitter said it sees these power users – which include companies, marketers and Twitter celebrities – as an “important constituency” and is going to “invest in the TweetDeck that users know and love.”

The deal for TweetDeck is the latest step by Twitter to round up important services that had been built around its fledgling product. The company has either purchased or built its own official mobile applications for iPhone, Android and BlackBerry, for example, and has said it no longer wants to leave crucial Twitter tools to outside developers.

This has caused consternation among the people who make tools that are based on the Twitter platform – like TweetDeck. In its announcement of the deal, Twitter said TweetDeck’s success and eventual purchase show there is “significant opportunity” for developers who make good tools.

Twitter co-founder Jack Dorsey also sees mainstream relevancy as a big challenge for the company. Mr. Dorsey, who had been pushed out of Twitter in 2008, returned as product chief of the company in March.